1. Field of the Invention
The invention is related to the field of magnetic sensing systems and, in particular, to fabricating a magnetic sensing chip having an extraordinary magnetoresistive (EMR) sensor and one or more transistors formed on the same substrate.
2. Statement of the Problem
A magnetoresistive (MR) read element based on extraordinary magnetoresistance (EMR) effect has been proposed for magnetic recording hard disk drives. Read elements based on EMR include an EMR sensor. The advantage of an EMR sensor over conventional giant magnetoresistive (GMR) sensors and tunneling magnetoresistive (TMR) sensors is that EMR is based on the Lorentz force, similar to devices based on the Hall effect. Thus, EMR sensors utilize nonmagnetic semiconducting materials rather than magnetic metals to detect magnetic fields, and therefore EMR sensors do not suffer from the problem of thermal magnetic noise or spin-torque noise.
An EMR sensor includes an EMR structure that is fabricated on a substrate as a mesa comprising a semiconductor heterostructure. A subset of the layers of the semiconductor heterostructure comprises a quantum well structure comprising a two-dimensional (2D) electron or hole gas, which is referred to as the EMR active region. A pair of voltage leads and a pair of current leads are formed on one side surface of the mesa in contact with the active region of the EMR structure, and an electrically conductive metal shunt is formed on an opposing side surface of the mesa in contact with the active region. In the absence of an applied magnetic field, injected current through the current leads passes into the active region and is shunted through the metal. When an applied magnetic field is present, current is deflected from the metal shunt and travels a longer distance through the semiconductor region. Because the semiconductor is much more resistive than the metal shunt, the electrical resistance of the device increases. The change in electrical resistance due to the applied magnetic field is detected across the voltage leads. EMR is described by T. Zhou et al., “Extraordinary magnetoresistance in externally shunted van der Pauw plates”, Appl. Phys. Lett., Vol. 78, No. 5, 29 Jan. 2001, pp. 667-669. An EMR sensor for recording head applications is described by S. A. Solin et al., “Nonmagnetic semiconductors as read-head sensors for ultra-high-density magnetic recording”, Appl. Phys. Lett., Vol. 80, No. 21, 27 May 2002, pp. 4012-4014.
Presently, EMR sensors are fabricated on a wafer substrate and then cut from the wafer to form individual EMR sensors. The voltage leads of an individual EMR sensor are then typically connected to a signal amplifier circuit to amplify data signals that are sensed by the EMR sensor. One problem with connecting the EMR sensor to the signal amplifier circuit is that the signal amplifier circuit is separately fabricated on a separate chip. The EMR sensor is typically connected to the separate signal amplifier circuit by electrically conductive wires. A capacitance is created between the electrically conductive wires, and the amount of capacitance is a function of the distance between the EMR sensor and the signal amplifier circuit. Additionally, the EMR sensing device typically has a resistance of a few hundred to a few thousand ohms, which is considerably higher than the 50 ohm standard impedance used for propagating high frequency signals. Thus, the capacitance and resistance can unfortunately reduce the signal being propagated to the signal amplifier circuit by RC roll-off because most remote low noise amplifiers require about 50 ohm impedance.